Defect Engineering for Modulating the Trap States in Two-dimensional Photoconductor

Defect induced trap states are essential in determining the performance of semiconductor photodetectors. The de-trap time of carriers from a deep trap could be prolonged by several orders of magnitude as compared to shallow trap, resulting in additional decay/response time of the device. Here, we demonstrate that the trap states in two-dimensional ReS₂ could be efficiently modulated by defect engineering through molecule decoration. The deep traps that greatly prolong the response time could be mostly filled by Protoporphyrin (H₂PP) molecules. At the same time, carrier recombination and shallow traps would in-turn play dominant roles in determining the decay time of the device, which can be several orders of magnitude faster than the as-prepared device. Moreover, the specific detectivity of the device is enhanced (as high as ~1.89×10¹³ Jones) due to the significant reduction of dark current through charge transfer between ReS₂ and molecules. Defect engineering of trap states therefore provides a solution to achieve photodetectors with both high responsivity and fast response.